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Results 451 - 500 of 2108
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RudziƄska Ewa - - 2007
Capillary electrophoresis was successfully applied for separation of the enantiomers of N-benzyloxycarbonyl-alpha-aminophosphonic and alpha-aminophosphinic acids as well as their ethyl and phenyl monoesters with the use of a range of commercially available cyclodextrins (alpha, beta and hydroxypropyl-gamma-cyclodextrins) as chiral selectors. The dependence of effectiveness of separation on type and concentration ...
Hyun Myung Ho - - 2007
A liquid chromatographic chiral stationary phase (CSP) based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6, which has been utilized in the resolution of alpha-amino acids, amines and amino alcohols, was treated with excess of n-octyltriethoxysilane to prepare a new improved CSP. The residual silanol groups of the original CSP were protected by n-octyl groups in ...
Lagarrigue Mélanie - - 2006
Capillary electrophoresis (CE) coupled to ion trap mass spectrometry (MS) was evaluated for the separation and identification of chemical warfare agent degradation products (alkylphosphonic acids and alkyl alkylphosphonic acids). Different analytical parameters were optimized in negative ionization mode such as electrolyte composition (15 mM CH(3)COONH(4), pH 8.8), sheath liquid composition ...
Siri Nathalie - - 2006
Naphthalene-2,3-dicarboxyaldehyde (NDA) is commonly used for detection of primary amines in conjunction with their separation with HPLC and CE. The fluorescence of the derivatives can be measured by a conventional fluorometer or via LIF. NDA is a reactive dye, which can replace o-phthaldehyde (OPA) and provides for derivatives which are ...
Hu Jiwei - - 2006
A hybrid silica monolithic stationary phase for RP CEC was prepared by in situ co-condensation of (3-mercaptopropyl)-trimethoxysilane (MPTMS), phenyltriethoxysilane (PTES), and tetraethoxysilane (TEOS) via a sol-gel process. The thiol groups on the surface of the stationary phase were oxidized to sulfonic acids by peroxytrifluoroacetic acid. The introduced sulfonic acid moieties ...
Qu Qishu - - 2006
An online preconcentration method based on electrostatic interaction between the analytes and inner surface of the capillary column was developed for the determination of zwitterionic analytes such as amino acids in CE coupled with a DAD. The amino acids possessed positive charges when they were dissolved in an acidic solvent. ...
Mydlová Janka - - 2006
In this paper, an HPLC method is used to determine the enantiomerization barrier of 2,3-pentadienedioic acid enantiomers. The racemate of 2,3-pentadienedioic acid was separated by HPLC on a chiral CHIROBIOTIC T column with a 90:10 (100:0.5:0.5 MeOH/HOAc/TEA)/H2O mobile phase. Peak areas of enantiomers prior to (A(+)0, A(-)0) and after the ...
Woontner Michael - - 2006
This unit describes methods for the preparation of samples for analysis of physiological amino acids and organic acids. Amino acids are analyzed by ion-exchange chromatography using an automated system. Organic acids are analyzed by gas-chromatography/mass spectrometry (GC-MS). Analysis of amino and organic acids is necessary to detect and monitor the ...
Huang Wen-Ying - - 2006
Angelicae Radix (AR) and Ligustici Rhizoma (LR) are both derived from the Umbelliferae plants and contain similar organic acids as their bioactive compounds. Nine of these organic acids, including nicotinic acid, protocatechuic acid, phthalic acid, folinic acid, p-hydroxybenzoic acid, folic acid, vanillic acid, caffeic acid, and ferulic acid were separated ...
Han Yanli - - 2006
An acid barrage stacking (ABS) method has been shown to be feasible for online anti-salt injection in CE of 9-fluorenylmethyl chloroformate (FMOC)-labeled amino acids (AAs) detected by common UV absorption. The operation was performed on normal polar CE by sucking in an extra plug of acid following a sample zone, ...
Zhang Song - - 2006
This work describes a highly enantioselective and sensitive immunosensor for the detection of chiral amino acids based on capacitive measurement. The sensor was prepared by first binding mercaptoacetic acid to the surface of a gold electrode, followed by modification with tyramine utilizing carbodiimide activation. The hapten 4-amino-D-phenylalanine was then covalently ...
Gong Xiao Yang - - 2006
The determination of the enantiomers of small non-UV-absorbing amines which otherwise can only be achieved with difficulty was possible by using a combination of the chiral crown ether (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) and dimethyl-beta-CD as selectors in CE and contactless conductivity measurement for detection. Alkylamines without any other functional group, amino ...
Huang Teng-Yi TY Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, - - 2006
A strategy is described and demonstrated for the formation of reagent anions via electrospray ionization (ESI) for electron-transfer dissociation (ETD). To circumvent difficulties associated with formation of high mass-to-charge ratio (m/z) reagent anions, it is desirable to form ETD reagents via means other than those that require reagent molecule vaporization. ...
Mayani Vishal J - - 2006
A new chiral stationary phase (CSP) was synthesized based on (S)-1-anilino-3-propyl-2-propanol covalently bonded to the mesoporous semi-crystalline material M41S. Direct semipreparative enantioseparation of mandelic acid could be achieved using medium pressure chromatography. Partly separated could also be the enantiomers of 2,2'-dihydroxy-1,1'-binaphthalene, cyanochromene oxide, diethyl tartrate and 2-phenyl propionic acid. The ...
Xiao Yan - - 2007
A mixture of five amino acids including arginine, histidine, phenylalanine, serine and glutamic acid was successfully separated in microchip capillary electrophoresis and detected with laser-induced fluorescence (LIF) detector. These amino acids were labeled with 5-(4, 6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF). The analyses were performed on two kinds of modified poly(dimethylsiloxane) (PDMS) microchips. ...
Li Ning - - 2007
The iCE280 Analyzer (iCE280) was evaluated for its potential application as a high-throughput tool to determine pI and separate charge related species using glycosylated, non-glycosylated and pegylated protein therapeutics as models. Resolution was achieved for glycosylated and non-glycosylated molecules, but remained a challenge for pegylated proteins. The sources of charge ...
Májek Pavel - - 2006
A classical kinetic method was used to determine the energy barrier for the inter-conversion of 2,3-pentadienedioic acid enantiomers. Each individual enantiomer was isolated by collecting the appropriate peaks from the HPLC enantiomeric separation, of racemic 2,3-pentadienedioic acid. The isolated enantiomers were racemized at 22 degrees C using various interconversion times. ...
Cheremina Olga - - 2006
Lumiracoxib {2-[(2-fluoro-6-chlorophenyl)amino]-5-methyl-benzeneacetic acid} is a highly selective and potent cyclooxygenase-2 (COX-2) inhibitor, which is chemically distinct from other coxibs in that it contains a carboxylic group and is weakly acidic. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with UV detection was validated and applied for the analysis ...
Rizvi Syed Asad Ali SA Department of Chemistry, Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, - - 2006
Two amino acid-derived (leucinol and N-methylpyrrolidinol) chiral ionic liquids are synthesized and characterized in both monomeric and polymeric forms. Leucinol-based chiral cationic surfactant is a room-temperature ionic liquid, and pyrrolidinol-based chiral cationic surfactant melts at 30-35 degrees C to form an ionic liquid (IL). The monomeric and polymeric ILs are ...
Al Bawab Abeer - - 2007
Topical formulations undergo radical structural changes after application and the action on the skin is not directly related to the original structure of the formulation. This fact has been well established in the scientific literature. However, and more essential, is the fact that these changes in the formulation structure are ...
Kakita Hirotaka - - 2006
To develop a fluorimetric high performance liquid chromatography (HPLC) technique for uronic acid microanalysis, a saline mobile phase and the postcolumn fluorimetric determination were combined. The detection limits of D-glucuronic, D-galacturonic and D-mannuronic acids were 7.19, 23.88 and 7.08 pmol, respectively. The proposed method was successfully applied to uronic acid ...
Zhang Hongyi - - 2006
An in-capillary derivatization of amino acids and peptides with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was developed for their subsequent capillary electrophoretic analysis with laser-induced fluorescence detection (lambda (ex)=488 nm). The in-capillary derivatization was achieved in zone-passing mode by introducing successive plugs of sample and NBD-F into a fused silica capillary previously equilibrated with ...
André Claire - - 2007
In this paper, the synthesis of a cyclic hexapeptide molecule was presented and evaluated for the enantiomer separation of a series of dansyl amino and arylalkanoic acids using high performance liquid chromatography (HPLC). It was clearly vizualized that this chiral selector allowed the separation of a great number of enantiomer ...
Cardinali Barbara - - 2006
Quantification of fibrinopeptides release is widely used to investigate fibrinogen activation, and standard chromatographic or capillary electrophoretic procedures are readily available. However, in the analyses of fibrinopeptide mixtures derived from the action of thrombin on human fibrinogen, a few unidentified peaks are usually present. The composition of these peaks was ...
Fradi Ines - - 2006
The enantiomeric separation of a series of acidic pharmaceuticals (mostly nonsteroidal anti-inflammatory drugs) has been investigated in NACE systems using single-isomer amino beta-CD derivatives. The first part of this study consisted of the selection of the basic experimental conditions to separate efficiently the enantiomers of acidic drugs. Several parameters, such ...
Gyllenhaal Olle - - 2006
In this paper, a chromatographic system based on carbon dioxide with methanol as mobile phase, and diol silica as stationary phase has been investigated for metoprolol and related amino alcohols by addition of strong acids to systems with triethylamine base as primary additive. Standard conditions used were 10% of methanol, ...
Zhao Shulin - - 2006
Abietic acid is a naturally occurring enantiomeric diterpenic acid. Its absolute optical purity and very stable stereochemistry structure makes it an excellent starting material for preparing chiral derivatizing reagents for chromatographic or electrophoretic applications. This paper describes the synthesis and evaluation of a novel chiral derivatization reagent, i.e., degradingdehydroabietylisothiocyanate (DDHAIC) ...
Schmid Martin G - - 2007
Particle-loaded monoliths containing a polymethacrylamide backbone were prepared by suspending a silica-based chiral phase in the mixture of the monomers followed by in-situ polymerization in the capillary. As chiral selector l-4-hydroxyproline chemically bonded to 3 microm silica particles was used following the separation principle of ligand-exchange. Electrolytes containing Cu(II) ions ...
Grant Suzanne L - - 2006
A simple and versatile methodology using high-performance liquid chromatography (HPLC) with fluorimetric detection was developed to simultaneously determine d-serine along with other metabolically related neuroactive amino acids in the glutamatergic system: L-serine, L-glutamate, L-glutamine, and glycine. On-column sensitivity was in the lower picomole range. Of two chiral thiol reagents investigated, ...
Rukhadze Marina D - - 2006
The chromatographic behaviour of compounds of biomedical significance was studied using micellar mobile phases modified with polyoxyethylene (20) sorbitan monooleate (Tween-80). The influence of the surfactant within the 0.75-4% concentration range on the retention factor of model compounds was investigated. The biological surfactant cholic acid was introduced into the mobile ...
Chen S - - 2006
Amino acids were derivatized with sulfur-containing reagents in alkaline medium and enantioresolved by HPLC on a teicoplanin chiral stationary phase. Much better resolution was achieved using methanol-based mobile phase compared with elution with acetonitrile-based solvent mixture. The value of selectivity factor for many derivatives examined in the study can be ...
Ye Yun K - - 2006
The enantioseparation of nine commercially available basic drugs was achieved on polysaccharide-based chiral stationary phases with the acidic additive ethanesulfonic acid and the basic additive butylamine. Seven different commercially available CSPs were used for the study (AD, AS, OD, OJ, OG, OB, and OC). Mobile phase additives have been proven ...
Huang Hsi-Ya - - 2006
In this study, anion-selective exhaustive injection-sweeping (ASEI-sweeping) technique, which is a selective on-line sample concentration technique, was first proposed in microemulsion electrokinetic chromatography (MEEKC) for analyses of eight acidic phenolic compounds. In contrast to a capillary that is typically filled with nonmicellar background solution in conventional ASEI-sweeping MEKC method, in ...
Natalini B - - 2006
S-benzyl-(R)-cysteine (R-SBC) is a new chiral ligand-exchange stationary phase which has proved to be effective in the analytical separation of some natural and unnatural underivatized amino acids with fair to good separation and resolution factors. The dynamic coating of the RP-18 solid support with S-Benzyl-(R)-cysteine (R-SBC) gives rise to a ...
Zeleke Jessica M - - 2006
Chiral immunoaffinity microbore columns were directly interfaced with MS detection, and the effect of column length and temperature on the enantiomer separation of a number of underivatized aromatic and aliphatic amino acids was investigated utilizing an antibody chiral stationary phase that had been prepared by immobilizing a monoclonal anti-D-amino acid ...
Ilisz István - - 2006
The application of a chiral ligand-exchange column (CLEC) for the direct high-performance liquid chromatographic enantioseparation of unusual secondary amino acids using D-penicillamine-Cu(II) complex as chiral selector is reported. The amino acids investigated were pyrrolidine-2-carboxylic acid, piperidine-2-carboxylic acid, piperazine-2-carboxylic acid, morpholine-3-carboxylic acid, and thiomorpholine-3-carboxylic acid analogs. Chromatographic results are given as ...
García-Villalba Rocío - - 2006
This study investigates the applicability of on-line coupling of capillary electrophoresis with electrospray ionization tandem mass spectrometry (CZE-ESI-MS) for the separation and characterization of alpha- and beta-acids and oxidized hop acids from crude extracts of different hop varieties. CZE-ESI-MS with negative-ion electrospray ionization proved to be a suitable technique for ...
Yongzhu Jin - - 2006
In order to develop a chiral stationary phase (CSP), which has even higher separation ability than the corresponding commercially available crown ether based CSP (OA-8000 having a pseudo-18-crown-6 ether with an OMe group as a selector), chemically bonded type CSP having a phenolic OH group on a crown ring was ...
Gioia M G - - 2006
The use of 2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1',5'-d]pyrazine-4,9-dione as pre-column reagent for LC analysis of amino acids is proposed. The compound reacts (30 min at 68 degrees C in presence of 0.04 M triethylamine in a dimethylsulfoxide-water mixture) with primary and secondary amino function and the stable resulting adducts can be chromatographed under reversed-phase ...
Gao Rong - - 2007
A novel HPLC-UV method was developed for the simultaneous determination of two major active components in Yinhuang injection, chlorogenic acid and baicalin, in rat plasma. Extracted from the plasma samples with methanol-acetonitrile (3:1, v/v), the two compounds were successfully separated using a C18 column with a gradient elution composed of ...
Drandarov Konstantin - - 2006
The first purely chemical method for automated no-carrier-added synthesis of [1-(11)C]-labeled d(R)- and l(S)-2-hydroxypropanoic acid (lactic acid) was developed for experimental neurophysiology studies and position emission tomography (PET) diagnosis. Starting from sodium 1-hydroxyethanesulfonate and [(11)C]HCN (trapped as [(11)C]KCN) the intermediate dl-(R,S)-[1-(11)C]-2-hydroxypropanenitrile was prepared. Its rapid acid hydrolysis gave dl-(R,S)-[1-(11)C]lactic acid, ...
Berkecz Róbert - - 2006
Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of 14 unnatural beta-amino acids, including several beta-3-homo-amino acids on a chiral stationary phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid bonded to 3-aminopropyl silica gel as chiral selector. The effects of the organic and the acidic modifiers and the mobile ...
Wójcik Lena - - 2006
Perfluorinated carboxylic acids (PFCAs) belong to anthropogenic fluoroorganic compounds that have been detected in the natural environment and living organisms including humans. A capillary zone electrophoretic method with indirect UV detection using 2,4-dinitrobenzoic acid (2,4-DNBA) as a chromophore probe has been developed for analysis of PFCAs (C6-C12) in water. Optimal ...
Wu Yu-Tse - - 2006
Salvianolic acid B is an herbal ingredient isolated from Salvia miltiorrhiza. The aim of this study was to apply an automated blood sampling system coupled to a simple liquid chromatographic system to determine the bioavailability of salvianolic acid B in stress-free rats. The plasma sample (25 microl) was vortex-mixed with ...
Yang Wen-Chu - - 2006
A new strategy for amino acid analysis is reported involving derivatization with an N-hydroxysuccinimide ester of N-alkylnicotinic acid (Cn-NA-NHS) followed by reversed-phase chromatography and electrospray ionization mass spectrometry (RPC-MS). Detection sensitivity increased as the N-alkyl chain length of the nicotinic acid derivatizing agent was increased from 1 to 4. N-Acylation ...
Liu Yueqi - - 2006
A novel chiral stationary phase based on chitosan covalently bonded onto silica gels has been prepared and used for the separation of various alpha-amino acid enantiomers as well as alpha-hydroxycarboxylic acid enantiomers by chiral ligand-exchange chromatography with copper(II) as a complexing ion. The methanol content and copper(II) ion concentration in ...
Carlavilla Davinia - - 2006
The formation of D-amino acids (D-aa's) in many fermented foods depends, among other factors, on the particular fermentation conditions, the action and autolysis of the microorganisms involved. In this sense, the analysis of chiral amino acids is an interesting analytical strategy for food scientists, since these compounds can be used ...
Tan Guanghui - - 2006
A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N-(substituted benzoyl)-alpha-amino acid amides and esters. N-(Substituted benzoyl)-alpha-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01:0.05:100, v/v/v) as an optimum mobile phase while N-(substituted benzoyl)-alpha-amino acid esters were not resolved ...
Ilisz István - - 2006
The search for new and effective chiral selectors capable of separating a wide variety of enantiomeric compounds is an ongoing process. In the past decade, macrocyclic antibiotics have proved to be an exceptionally useful class of chiral selectors for the separation of enantiomers of biological and pharmacological importance by means ...
Kubán Pavel - - 2006
The application of gradient methods in HPLC determinations with capacitively coupled contactless conductivity detection was successfully demonstrated for non-UV-absorbing amino acids as well as for small peptides as analytes. The drift in baseline which is caused by the change in the conductivity of the mobile phase during the elution could ...
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